how to connect to Sites with Two ISP

Khurram Tariq · ‎02-06-2016

Dear All

i have a question about connecting two sites Site A(Head office) Site B(Branch office), currently we are connected with one ISP by using static routes to ISP local ip like 172.16.10.1 is site A gateway and 192.16.10.1 is site B gateway.we have static routes for destination 172.16.10.1 and 192.16.10.1 for each site.all the services are working fine with one ISP.Now we need to add second ISP for redundancy and load sharing purpose for the connectivity between site A and Site B.

please help me how to get this working in our office we are using cisco 3945 routers to connect with isp at each site.

please help

Tagir Temirgaliyev · ‎02-06-2016

you can use routing protocol like rip ospf bgp or ip sla and even static routes over gre tunnels

Khurram Tariq · ‎02-07-2016

Thanks for your reply ,

can you explain more how to achieve this with IP sla static routes and we are not using default routes , using only static routes

Tod Larson · ‎02-07-2016

The good news is you've got a zillion options. I just throw out some ideas for you to think about.

What WAN connection do you have? T1, point to point ethernet, MPLS? Can you peer with the ISP using OSFP?

What new WAN connection are you adding?

How many 3945 router are at the Head Office and how many are at the Brand Office?

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if you have point to point connections then you could do layer 3 LACP.

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A "Floating Static" route is a good way allow your 3945 router to use a static route and then failover to a backup static. However that by itself doesn't achieve load balancing. Load balance with floating static routes would be to manually create 2 sets of floating static routes based on whatever destination subnets you want to you. This gets pretty complicated pretty fast, so you'd want to consider a routing protocol

https://www.freeccnaworkbook.com/workbooks/ccna/configuring-a-floating-static-route

http://howdoesinternetwork.com/2013/static-floating-route

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You could have simply use 2 static routes for per packet load balancing. Static route 1 pointed to ispA and Static route 2 pointed to ispB. This will give you per packet load balancing (which may or may not be good for your applications).

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I recommend this set of design guides for all the commands references. The rub is that none of these will recommend static routing.

http://www.cisco.com/c/en/us/solutions/enterprise/design-zone-branch-wan/index.html#~designs

Khurram Tariq · ‎02-07-2016

Thanks Tod Larson for the reply

well

What WAN connection do you have? T1, point to point ethernet, MPLS? Can you peer with the ISP using OSFP: i dont know

What new WAN connection are you adding:its the same mpls l3

How many 3945 router are at the Head Office and how many are at the Brand Office?one 3945 at head office and same at remote office.

forget about load balancing , if i want to use one subnet on one isp and other subnet on other isp. if any isp down traffic goes to other ISP,

one idea is to create GRE tunnel with remote office on both ISP's and then use floating method with ip sla to shift traffic and with pbr can route subnets to any tunnel.

what would you say about this will it wrork ?

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Tagir Temirgaliyev · ‎02-08-2016

https://supportforums.cisco.com/document/13576/how-configure-gre-tunnel

Tod Larson · ‎02-10-2016

Yes, the gre tunnel approach would work.

Here is a simple scenario done with static routes (no gre tunnels) that might meet your needs. It's redundant and shares the load between ISPs. Perhaps you can adjust this to your needs.

Head office router

g0/1- ISP 1, ip 10.1.1.1 gw 10.1.1.2

g0/2 - ISP 2, ip 10.1.2.1 gw 10.1.2.2

g0/3 - LAN 1, 10.1.11.1/24

g0/3 - LAN 2, 10.1.22.1/24

ip route 10.2.11.0 255.255.255.0 10.1.1.2

ip route 10.2.11.0 255.255.255.0 10.1.2.2 10 <-- this is a "backup" route

ip route 10.2.22.0 255.255.255.0 10.1.2.2

ip route 10.2.22.0 255.255.255.0 10.1.2.2 10 <-- this is a "backup" route

Branch office router

g0/1- ISP 1, ip 10.2.1.1 gw 10.2.1.2

g0/2 - ISP 2, ip 10.2.2.1 gw 10.2.2.2

g0/3 - LAN 1, 10.2.11.1/24

g0/3 - LAN 2, 10.2.22.1/24

ip route 10.1.11.0 255.255.255.0 10.2.1.2

ip route 10.1.11.0 255.255.255.0 10.2.2.2 10 <-- this is a "backup" route

ip route 10.1.22.0 255.255.255.0 10.2.2.2

ip route 10.1.22.0 255.255.255.0 10.2.1.2 10 <-- this is a "backup" route